We plan to investigate the pathogenesis of capillary aneurysms and other retinal abnormalities typical of human diabetes mellitus which have been observed by us in dogs and rhesus monkeys made diabetic experimentally. The evolution of retinopathy in experimental diabetes is to be documented clinically by means of ophthalmoscopy, fluorescein angiography, and color fundus photography, and the observations are to be compared with the histology and metabolism of the retina and its vessels at various durations of diabetes. Microvascular and metabolic abnormalities observed in alloxan diabetic dogs will be compared with effects of diabetes surgically induced by pancreatectomy. Experimental procedures by which the development of retinopathy may perhaps be inhibited are to be explored, and the relationship of the angiopathy to diabetes control is to be assessed.